I'm new to the BI space and have been asked to look into using cubes without building a datawarehouse or otherwise restructuring the current reporting database that is in use. Everything I've seen in the way of articles and tutorials about cubes use the AdventureWorksDW database and nothing has used a relational model. Is it possible to build cubes of relational tables? I'm guessing the performance would be abysmal but I'm not certain. Would this solution, if possible, suffice for a small number of users (like 5) doing ad hoc reporting?

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Why DONT you want to build a DW? apart from a pretty steep learning curve, I don't think there is any licencing issue with R2

you can build pivots for specific datasets, or you may be better off connecting XL to the R2 database and using pivot tables

A lot of cube type analysis can be done in SSRS as well.

How big is your data, how GOOD is your data and how well indexed are your tables. On the primary tables, are you mainly inserting records or are there a lot of updates and deletes as well. Is the database OLTP (transactional) or OLAP (analysis and reporting)

Do users need to be able to summarise and drill down in many different ways, or do they just want pretty reports. If the latter, then SSAS may be overkill, you can do the same using nise SSRS reports.